The invention relates to recognizing voice in a noisy environment and more specifically to elements controlled by voice initiations.
A generic method can be derived from the operation of a device known from DE-OS 36 10 797 or U.S. Pat. No. 4,625,083. This already contains a voice microphone and an ambient noise microphone the signals of which are brought into relation to one another by electric subtraction. During the subtraction, the noise components applied equally to the two microphones--particularly ambient noises--are eliminated so that the resulting residual signals can be easily comprehended as voice commands. The beginning of the voice signal remaining after the subtraction is intended to produce, for example, a change-over of a hand-free telephone from receiving to transmitting mode only if really required.
To keep the proportion of voice sound applied to the ambient noise microphone when the operating person is speaking as low as possible, the ambient noise microphone must be arranged at some distance from the mouth of the operating person. The result of this is, however, that the ambient noise level at the ambient noise microphone does not necessarily correspond to that at the voice microphone so that even without voice being applied to the voice microphone, the result of the subtraction of the signals of the two microphones always switched to readiness to transmit must not always be equal to zero. This is why control errors cannot be excluded even here.
Furthermore, other devices with comparable function are known which only switch a single voice microphone each to readiness to transmit under particular conditions.
This is done in generally known manner by a transmit key being manually operated by the microphone user.
From GB-A 2003 002, a device is know which automatically closes a transmitter switch when the microphone input level suddenly rises.
In DE-OS 34 01 883, the proposal is disclosed to switch a microphone to readiness to transmit by a proximity sensor which detects the approach of the head of the operating Person to the microphone for speaking.
In all these devices, only one (voice) microphone is always used.
In U.S. Pat. No. 3,383,466 non-acoustic parameters are measured and used in a speech recognition system. Larynx vibration and nasal sounds are measured by microphones, lips are read optically and air velocity is measured by an anemometer.
The present invention has the object of specifying a method by which an interpretation of pure ambient noises as the beginning of a voice command can be eliminated by using a sound which is predominantly generated during speaking and a microphone to which at least ambient noises are applied, and of suitably constructing the generic device for carrying out the method according to the invention.
According to the invention, this object is achieved by the following.
Since contact sound generated during speaking can be picked up with extremely short time delay at the head or neck, particularly at the throat of the operating person, a signal generated by a direct-contact microphone is very suitable for detecting the beginning of a voice command. The actual voice microphone, to which ambient noises are also applied, can be electrically switched on by the contact sound signal for voice signal transmission exactly at the time of the beginning of the voice command without possibility of error. During this process, the operating person does not need to make any deliberate hand or head movement because both microphones can be carried in suitable harnesses in accordance with a development of the device. Neither is the operator impeded in any sequences of movements, especially not if furthermore a portable transmitter is also provided which transmits the voice commands by wireless means to an appropriate receiver.
Although the electric signals of the direct-contact microphone alone are not sufficient for voice recognition since they cannot reproduce, for example, any formants and nasal sounds, they can further enhance the transmitted voice pattern of the voice microphone if they are suitable combined with the electric signals of the voice microphone, for example by phase-synchronous addition.
It is furthermore advantageous that the voice microphone is automatically switched off whenever speech pauses arise. The switch-on duration can also be automatically restricted to the permissible word reception duration of the voice recognition circuit. In the switch-on case, a signal is supplied to the operating person.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.